Abstract: We investigated the effects of biochar application on nitrous oxide (N₂O) emission in tobaccoplanted soils by laboratory incubation experiment and meta-analysis. There were six treatments in the incubation experiment: no nitrogen fertilizer and no biochar application (N0B0), no nitrogen fertilizer but biochar application (N0B100), nitrogen fertilizer but no biochar application (N100B0), reducing nitrogen fertilizer by 20% and no biochar application (N80B0), nitrogen fertilizer and biochar application (N100B100), and reducing nitrogen fertilizer by 20% and biochar application (N80B100). N₂O fluxes, ammonium (NH₄⁺) and nitrate (NO₃^-) contents were measured. Furthermore, a meta-analysis was performed to explore the optimal fertilization and biochar application rates to reduce N₂O emissions from tobacco-planted soils using data from 10 peer-reviewed papers. Results showed that: (1) N₂O fluxes of each treatment decreased rapidly and tended to be stable during the incubation duration. Compared with N0B0 treatment, nitrogen fertilization significantly increased cumulative N₂O emissions. Compared with N100B0 (or N100B100) treatment, N80B0 (or N80B100) treatment significantly reduced the cumulative N₂O emission. (2) During the whole incubation period, biochar application significantly reduced N₂O emission under the same nitrogen fertilizer application level. (3) N₂O emissions positively correlated with NH₄⁺ content, and negatively correlated with NO₃^- content. (4) Compared with other crop systems, N²O emission factors (EFs) in the tobacco-planted system are relatively smaller. Nitrogen fertilizer reduction and biochar application could significantly mitigate N₂O emission from tobacco-planted soils. These findings provide a theoretical basis for optimizing fertilization strategies and biochar implementation to reduce N₂O emissions from tobacco-planted systems, with important significance for realizing carbon neutrality and sustainable agricultural development in agricultural ecosystems.

Key words: biochar, greenhouse gas, tobacco field, meta-analysis, agricultural carbon neutrality